Field of the Invention
The invention relates in general to a sequence estimation device and method, and more particularly to a sequence estimation device and method capable of reducing error propagation and having a low complexity level.
Description of the Related Art
Video broadcasting standards include Advanced Television System Committee (ATSC) in the U.S., Digital Video Broadcasting—Terrestrial (DVB-T) in Europe, Integrated Services Digital Broadcasting—Terrestrial (ISDB-T) in Japan, and Digital Terrestrial Multimedia Broadcast (DTMB) in China. In a digital communication system, a signal is affected by multi-path fading when transmitted via a wireless channel, and inter-symbol interference (ISI) is generated such that a receiver may not correctly recover the signal. To eliminate ISI, a receiver is usually provided with an equalizer and a sequence estimation device to estimate the transmitted signal.
Common equalizers include linear feedforward equalizers (LFEs) and decision feedback equalizers (DFEs). However, LFEs suffer from a drawback of reinforced noise, whereas DFEs also suffer from a drawback of error propagation. That is to say, when a decision is incorrect, a DFE nonetheless performs equalization on a received signal, in a way that the performance of the equalizer is reduced and more incorrect decisions are made.
On the other hand, according to received signals and all possible sequence combinations of the signals, a sequence estimation device selects a most probable signal combination. However, when the number of symbols crossed by ISI is large (e.g., when the channel is length is long) or when a modulation level of transmitted signals is high, the computation complexity of the sequence estimation device may exponentially increase. In short, when a transmitted signal has an Mth-order modulation level and a channel length of L, the complexity level is ML. For example, in the DMTB standard, assuming that M is 32 and L is only 5, the complexity level of the sequence estimation device is about 325—such complexity level produces enormous power consumption.
Therefore, there is a need for a solution for solving error propagation and reducing the complexity level of a sequence estimation device.